Problem with S4315R Continuous Servos


I recently bought a pair of SpringRC SM-SR4315R high-torque continuous rotation servos to upgrade some similar Parallax servos.

Both servos are run off of the same control line on pin 9 off of an Arduino and share a 6V power supply (1200 mA).

The new servos aren’t responding to my control signals correctly. They will go counterclockwise, but they won’t stop at 1500 microseconds and they won’t change speed. Oddly enough, the only way I could get them to stop running was when I did a DigitalWrite to an LED run off of pin 11. When the light goes on, the servos stop running for some reason. I should mention that adjusting the centering pin has no effect.

The only thing I can think is that there is some electrical interference, or that they draw more current than something can handle. The old servos still work fine with the same sketch and circuit. I’ve simplified the sketch to just send a stop signal, but no luck.

Any ideas?


We do not have experience with those particular servos, but you might try testing them with something like an RC receiver to see if they behave as you expect. Probing the output from your Arduino with an oscilloscope could help determine whether it is sending valid pulses. Also, the minimum recommended input voltage for an Arduino UNO board is 7V so if your input voltage is sagging, it could cause odd behavior. It is possible that the new servos could have more demanding power requirements than the older ones, so it might be necessary to use a higher capacity power supply.